WO2009016656A1 - Thin-film multilayer treatment for bidirectional attenuation of stray light - Google Patents

Thin-film multilayer treatment for bidirectional attenuation of stray light Download PDF

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Publication number
WO2009016656A1
WO2009016656A1 PCT/IT2007/000535 IT2007000535W WO2009016656A1 WO 2009016656 A1 WO2009016656 A1 WO 2009016656A1 IT 2007000535 W IT2007000535 W IT 2007000535W WO 2009016656 A1 WO2009016656 A1 WO 2009016656A1
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WO
WIPO (PCT)
Prior art keywords
thin
treatment
multilayer
multilayer treatment
optical
Prior art date
Application number
PCT/IT2007/000535
Other languages
French (fr)
Inventor
Paolo Lagana'
Leonardo Chicarella
Marco Barilli
Original Assignee
Galileo Avionica S.P.A.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Galileo Avionica S.P.A. filed Critical Galileo Avionica S.P.A.
Priority to PCT/IT2007/000535 priority Critical patent/WO2009016656A1/en
Publication of WO2009016656A1 publication Critical patent/WO2009016656A1/en

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Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/20—Filters
    • G02B5/28—Interference filters
    • G02B5/285—Interference filters comprising deposited thin solid films
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/0018—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 with means for preventing ghost images
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/005—Diaphragms

Definitions

  • the present invention relates to a thin-film multilayer treatment for bidirectional attenuation of straylight.
  • residual radiation In optical systems the mutual non-sequential interaction between luminous radiation, optical parts and mechanical edges of said optical parts generates a residual radiation which negatively affects the quality of the image archived. Said residual radiation is referred to by the term “residual light", “parasite light” or, more correctly, "straylight”.
  • the methods currently employed to reduce the phenomenon of straylight are based on the use of mechanical diaphragms.
  • Said diaphragms provided by means of complex machining on the inner part of the lenses and positioned between the various optical parts, absorb the residual radiation resulting from the multiple reflections thereof on their edges.
  • the diaphragm darkening treatment generally entails a thickening of the "tips" of the diaphragms, again limiting efficiency.
  • the aim of the present invention is to produce a system for the suppression of straylight, the technical characteristics of which are such as to overcome the drawbacks of the known art.
  • the subject of the present invention is a thin-film multilayer treatment applied by deposition onto an optical support; said multilayer treatment being characterised in that it comprises a plurality of thin films consisting alternately of a dielectric material and a metal or metal alloy; said dielectric material and said metal or said metal alloy being chosen according to wavelength interval of interest and mutual compatibility.
  • figure 1 is a prospective overhead view of the optical component to which the multilayer treatment subject of the present invention has been applied; and figure 2 contains four graphs showing the reflectance measurements of the multilayer treatment subject of the present invention deposited on an optical support.
  • an optical component on which the treatment subject of the present invention has been performed is indicated overall by 1.
  • the optical component 1 comprises an optical support 2 and a thin-film multilayer 3 applied to the optical support 2 like a circular mask.
  • the thin-film multilayer 3 is made of 15 thin films consisting alternately of SiO 2 and a metal alloy based on Ni and Cr .
  • the optical component 1 has a high efficiency in elimination of the straylight due to the characteristic of opacity of the thin-film multilayer 3 in terms of both transmitted radiation and reflected radiation.
  • This opacity characteristic is bidirectional, which means that it occurs both when the radiation follows the sequential air-multilayer-substrate path and when the radiation follows the sequential substrate- multilayer-air path.
  • the thin films have been deposited by means of the technique of e-gun evaporation.
  • the particular deposition technique used does not constitute in any way a limitation to the present invention.
  • another deposition technique that could be used is the technique of sputtering.
  • Figure ' 2 illustrates four graphs which show the reflectance measurements of tests performed on the multilayer treatment of an optical support.
  • the measurements were performed using wavelength radiations from 400 to 1100 nm, from both directions and with different angles of incidence.
  • the graph 2a shows the results of reflectance of a radiation with angle of incidence of 0° (normal at the surface of the optical component) and with an air-multilayer- substrate optical path
  • the graph 2b shows the reflectance results of a radiation with angle of incidence of 0° (normal at the surface of the optical component) and with a substrate- multilayer-air optical path
  • the graph 2c shows the reflectance results (mean polarisation) of a radiation with angle of incidence of 20° and 45° respectively and with an air-multilayer-substrate optical path
  • the graph 2d shows the reflectance results (mean polarisation) of a radiation with angle of incidence of 20° and 45° respectively and with a substrate-multilayer-air optical path.
  • the multilayer treatment of the present invention guarantees a very low reflectivity at different angles of incidence of the incident radiation.
  • the multilayer treatment subject of the present invention is more efficient than mechanical diaphragms, as it definitively eliminates the problem of the limited minimum dimensions that can be achieved, with consequent limits in reduction of the straylight, and has optical characteristics of opacity which could otherwise be obtained only by very costly darkening treatments .
  • the multilayer treatment subject of the present invention is better than the conventional darkening treatments (reflectance in the order of 4% for Electrodag 502 coating, 7% for anode type darkening) .
  • the multilayer treatment subject of the present invention reduces the mass of the optical system eliminating the mechanical diaphragms, and permits the sizing of light traps with high absorbance for the infrared visible/near radiation.
  • the conventional darkening treatment it has a "specular” and not “propagating" type behaviour vis-a-vis the radiation.
  • the multilayer treatment subject of the present invention attenuates straylight bidirectionally, with the consequent advantage of permitting application of the thin-film multilayer on one only of the two surfaces of the optical support, thus avoiding the treatment of both.

Abstract

A thin-film multilayer treatment (3) for bidirectional attenuation of straylight applied by means of deposition on an optical support (2) and comprising a plurality of thin films consisting alternately of a dielectric material and a metal or metal alloy. The dielectric material and the metal or metal alloy are chosen according to wavelength interval of interest and mutual compatibility.

Description

THIN-FILM MULTILAYER TREATMENT FOR BIDIRECTIONAL ATTENUATION OF STRAY LIGHT
TECHNICAL FIELD The present invention relates to a thin-film multilayer treatment for bidirectional attenuation of straylight.
BACKGROUND ART
In optical systems the mutual non-sequential interaction between luminous radiation, optical parts and mechanical edges of said optical parts generates a residual radiation which negatively affects the quality of the image archived. Said residual radiation is referred to by the term "residual light", "parasite light" or, more correctly, "straylight".
The methods currently employed to reduce the phenomenon of straylight are based on the use of mechanical diaphragms. Said diaphragms, provided by means of complex machining on the inner part of the lenses and positioned between the various optical parts, absorb the residual radiation resulting from the multiple reflections thereof on their edges.
Although this solution guarantees considerable attenuation of the straylight, it suffers from the drawback of requiring complex and laborious machining work, followed by their darkening treatment. Furthermore, the "tips" of the diaphragms, however tapered they are, have dimensions in the order of a few tenths of a micron, which for high performance straylight reduction applications represent a limit in terms of efficiency. In this regard, it should be added that the diaphragm darkening treatment generally entails a thickening of the "tips" of the diaphragms, again limiting efficiency.
DISCLOSURE OF INVENTION The aim of the present invention is to produce a system for the suppression of straylight, the technical characteristics of which are such as to overcome the drawbacks of the known art.
The subject of the present invention is a thin-film multilayer treatment applied by deposition onto an optical support; said multilayer treatment being characterised in that it comprises a plurality of thin films consisting alternately of a dielectric material and a metal or metal alloy; said dielectric material and said metal or said metal alloy being chosen according to wavelength interval of interest and mutual compatibility.
BRIEF DESCRIPTION OF THE DRAWINGS
The following example is provided for illustrative non- limiting purposes, for a better understanding of the invention with the help of the figures of the accompanying drawing, in which: figure 1 is a prospective overhead view of the optical component to which the multilayer treatment subject of the present invention has been applied; and figure 2 contains four graphs showing the reflectance measurements of the multilayer treatment subject of the present invention deposited on an optical support.
BEST MODE FOR CARRYING OUT THE INVENTION
In figure 1, an optical component on which the treatment subject of the present invention has been performed is indicated overall by 1.
The optical component 1 comprises an optical support 2 and a thin-film multilayer 3 applied to the optical support 2 like a circular mask. The thin-film multilayer 3 is made of 15 thin films consisting alternately of SiO2 and a metal alloy based on Ni and Cr .
The optical component 1 has a high efficiency in elimination of the straylight due to the characteristic of opacity of the thin-film multilayer 3 in terms of both transmitted radiation and reflected radiation. This opacity characteristic is bidirectional, which means that it occurs both when the radiation follows the sequential air-multilayer-substrate path and when the radiation follows the sequential substrate- multilayer-air path.
In the specific example the thin films have been deposited by means of the technique of e-gun evaporation. However, the particular deposition technique used does not constitute in any way a limitation to the present invention. For example, another deposition technique that could be used is the technique of sputtering.
Figure' 2 illustrates four graphs which show the reflectance measurements of tests performed on the multilayer treatment of an optical support.
The measurements were performed using wavelength radiations from 400 to 1100 nm, from both directions and with different angles of incidence.
In particular, the graph 2a shows the results of reflectance of a radiation with angle of incidence of 0° (normal at the surface of the optical component) and with an air-multilayer- substrate optical path; the graph 2b shows the reflectance results of a radiation with angle of incidence of 0° (normal at the surface of the optical component) and with a substrate- multilayer-air optical path; the graph 2c shows the reflectance results (mean polarisation) of a radiation with angle of incidence of 20° and 45° respectively and with an air-multilayer-substrate optical path; the graph 2d shows the reflectance results (mean polarisation) of a radiation with angle of incidence of 20° and 45° respectively and with a substrate-multilayer-air optical path. As can be seen from the graphs of figure 2, the multilayer treatment of the present invention guarantees a very low reflectivity at different angles of incidence of the incident radiation.
Analogous data in trasparency have not been available since reduction of the component during transmission is such (T<10~5) that it cannot be measured with the ordinary laboratory spectrophotometers.
The multilayer treatment subject of the present invention is more efficient than mechanical diaphragms, as it definitively eliminates the problem of the limited minimum dimensions that can be achieved, with consequent limits in reduction of the straylight, and has optical characteristics of opacity which could otherwise be obtained only by very costly darkening treatments .
In particular, the multilayer treatment subject of the present invention is better than the conventional darkening treatments (reflectance in the order of 4% for Electrodag 502 coating, 7% for anode type darkening) .
Furthermore, the multilayer treatment subject of the present invention reduces the mass of the optical system eliminating the mechanical diaphragms, and permits the sizing of light traps with high absorbance for the infrared visible/near radiation. In fact, unlike the conventional darkening treatment, it has a "specular" and not "propagating" type behaviour vis-a-vis the radiation. Such an advantage facilitates the work of the optical design engineer in defining the light trap according to trajectories deterministically obtained from the law of reflection.
Lastly, it should be highlighted that the multilayer treatment subject of the present invention attenuates straylight bidirectionally, with the consequent advantage of permitting application of the thin-film multilayer on one only of the two surfaces of the optical support, thus avoiding the treatment of both.

Claims

- S -CLAIMS
1. Thin-film multilayer treatment (3) applied by means of deposition on ' an optical support (2) ; said multilayer treatment (3) being characterised in that it comprises a plurality of thin films consisting alternately of a dielectric material and a metal or metal alloy; said dielectric material and said metal or metal alloy being chosen according to wavelength interval of interest and mutual compatibility.
2. Multilayer treatment as claimed in claim 1, characterised in that said dielectric material is SiO2.
3. Multilayer treatment as claimed in claim 1 or 2, characterised in that said metal alloy is based on Ni and Cr.
4. Optical component (1) comprising an optical support (2) and a multilayer treatment (3) according to any one of the preceding claims .
PCT/IT2007/000535 2007-07-27 2007-07-27 Thin-film multilayer treatment for bidirectional attenuation of stray light WO2009016656A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
PCT/IT2007/000535 WO2009016656A1 (en) 2007-07-27 2007-07-27 Thin-film multilayer treatment for bidirectional attenuation of stray light

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/IT2007/000535 WO2009016656A1 (en) 2007-07-27 2007-07-27 Thin-film multilayer treatment for bidirectional attenuation of stray light

Publications (1)

Publication Number Publication Date
WO2009016656A1 true WO2009016656A1 (en) 2009-02-05

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Country Status (1)

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WO (1) WO2009016656A1 (en)

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5568322A (en) * 1993-03-02 1996-10-22 Asahi Kogaku Kogyo Kabushiki Kaisha Image forming lens system
EP0833172A2 (en) * 1996-09-26 1998-04-01 Matsushita Electric Industrial Co., Ltd Light absorber and optical equipment
EP1124143A2 (en) * 2000-02-10 2001-08-16 Matsushita Electric Industrial Co., Ltd. Lens, manufacturing method thereof, and optical device using the same lens
US20020030898A1 (en) * 2000-09-04 2002-03-14 Akira Kouchiyama Optical device, method for producing the same and recording and/or reproducing
US20040027706A1 (en) * 2002-06-28 2004-02-12 Katsura Nakajima ND filter and aperture device including the same
US20040247906A1 (en) * 2002-05-24 2004-12-09 Optical Coating Laboratory, Inc., A Jds Uniphase Company Coating for forming a high definition aperture

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5568322A (en) * 1993-03-02 1996-10-22 Asahi Kogaku Kogyo Kabushiki Kaisha Image forming lens system
EP0833172A2 (en) * 1996-09-26 1998-04-01 Matsushita Electric Industrial Co., Ltd Light absorber and optical equipment
EP1124143A2 (en) * 2000-02-10 2001-08-16 Matsushita Electric Industrial Co., Ltd. Lens, manufacturing method thereof, and optical device using the same lens
US20020030898A1 (en) * 2000-09-04 2002-03-14 Akira Kouchiyama Optical device, method for producing the same and recording and/or reproducing
US20040247906A1 (en) * 2002-05-24 2004-12-09 Optical Coating Laboratory, Inc., A Jds Uniphase Company Coating for forming a high definition aperture
US20040027706A1 (en) * 2002-06-28 2004-02-12 Katsura Nakajima ND filter and aperture device including the same

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